Possible, but they you have to balance this risks:
the less places your bitcoins are stored at, the more likely you'll lose your coins (robbery, defective media, fire, flood, ...)
the more places your bitcoins are stored at, the more likely you'll lose your coins if someone steals it - though a strong password on the data can thwart that quite effectively (unless you forget the password of course - if the box is in storage for few years and you have not written the password down - there may be quite some trouble remembering what actually have you used as the password).
Every time you unlock your wallet you train memory of the passphrase. I kow from experience that a passphrased used for 6 months on a regular basis will probably never be forgotten by me. I have recalled passphrases not used for 5 years just because I used them a lot back then.